In level sensors that operate in accordance with the FMCW (Frequency Modulated Continuous Wave) or the pulse-time delay principle, electromagnetic or acoustic waves are emitted in the direction of a product surface. Subsequently, a sensor records the echo signals reflected by the product, i.e., the filling medium, the container fixtures and the container itself and derives the location or position of a surface of at least one product situated in the container from the recorded echo signals.
When using acoustic or optical waves, the signal generated by the level gauge generally propagates freely in the direction of the product surface to be measured. In devices that utilize radar waves for measuring the product surface, the radar waves may either propagate freely in the direction of the medium to be measured or in the interior of a hollow waveguide that guides the radar waves from the level gauge to the medium. In devices that operate in accordance with the guided microwave principle, the high-frequency signals are guided to the medium along a waveguide.
The arriving signals are reflected on the surface of the medium or product to be measured and once again arrive at the level gauge after a corresponding transit time. The level gauge receives the signals reflected at different locations and determines the distance to the product thereof
The determined distance to the product is transmitted to an external location. The transmission may be realized in analog form, for example, by means of a 4 . . . 20 mA interface or in digital form, for example, by means of a fieldbus protocol.
A tracking method may be utilized in order to group echoes of successive echo curves that result from identical reflection points respectively. However, it may be difficult to correctly allocate an echo to a certain track.